The congenital adrenal hyperplasia, especially 21-hydroxylase deficiency, are common inherited disorders of steroidogenesis. Correlation of phenotype with genotype, which was made possible by this protocol has established reasonably good phenotype-genotype correlation. However, phenotypic heterogeneity occurs especially among individuals carrying either the intron 2 splicing mutation or the I172N missense mutation. Current studies focus on: 1) investigation into the molecular basis of phenotypic heterogeneity of the splicing mutation by examining the role of positive and negative splicing factors; 2) investigation of the possible heterozygous advantage of CAH through correlation of presence of auto-antibodies with mutation status; and 3) development of protocols to increase through-put for CYP21 molecular genetic analysis.